The present invention relates in general to a method of finishing inner circumferential surfaces of a plurality of holes, which are arranged along a line and spaced apart from each other in the axial direction of the holes, and a reamer suitable for the same method.
There is a demand for finishing inner circumferential surfaces of a plurality of holes, such as camshaft holes of an engine, which are arranged along a line and axially spaced apart from each other, with a high degree of concentricity between the holes and a high degree of dimensional accuracy of each hole. To satisfy such a demand, there has been conventionally employed a single-blade reamer having a cutting tip fixedly attached to the tool body, or a cutting tip slidably attached to the tool body such that the position of the cutting tip relative to the tool body is finely adjustable by an adjusting mechanism which is built in the tool body. It is preferable that the single-blade reamer has a plurality of land surfaces formed in an outer circumferential surface thereof and axially extending from a distal end thereof toward a proximal end thereof, and that the cutting tip having major and minor cutting edges is positioned in one of the land surfaces. Further, it is desirable that the cutting tip is constituted by a sintered-compact cutting tip or other cutting tip which has a hardness higher than that of cemented carbide.
However, where the demand is very severe, namely, where the required degrees of concentricity and dimensional accuracy are considerably high, it is not easy to satisfy such a severe demand even by using the above-described reamer.
The present invention was made under this situation, and the object of the invention is therefore to provide a method of finishing inner circumferential surfaces of a plurality of holes which are arranged along a line and spaced apart from each other in the axial direction of the holes, and a reamer suitable for practicing the same method, which assure a required degree of concentricity between the holes and a required degree of dimensional accuracy of each hole even where the required degrees of concentricity and dimensional accuracy are considerably high.
The present invention provides an inner-circumferential-surface finishing method or a reamer according to each of the following modes of the invention, which are numbered and dependent from each other like the appended claims, where appropriate. It is to be understood that the following modes are provided to facilitate the understanding of possible combinations of features recited in the following modes, and that the technical features and the combinations of the technical features disclosed in the present specification are not limited to the following modes.
(1) A method of finishing inner circumferential surfaces of a plurality of holes which are arranged along a line and spaced apart from each other in an axial direction of the plurality of holes by using a reamer, the method being characterized in that:
the reamer comprises at least one land surface which is formed in an outer circumferential surface of the reamer and which extends from an axially distal end of the reamer toward an axially proximal end of the reamer, an axially-distal-end small-diameter portion which extends over a predetermined axial distance from the axially distal end toward the axially proximal end, a guide portion which is axially adjacent to the axially-distal-end small-diameter portion, and major and minor cutting edges which are formed in at least one of the at least one land surface in the axially-distal-end small-diameter portion, the at least one land surface having a turning radius which is smaller in the axially-distal-end small-diameter portion than in the guide portion, the minor cutting edge having a turning radius which is larger than the turning radius of the at least one land surface in the axially-distal-end small-diameter portion and which is smaller than the turning radius of the at least one land surface in the guide portion;
and wherein the plurality of holes are finished in order of the arrangement of the plurality of holes in the line, such that an inner circumferential surface of an outermost one of the plurality of holes is first finished by the major and minor cutting edges of the reamer, and such that an inner circumferential surface of each of the other of the plurality of holes is then finished by the major and minor cutting edges, with the guide portion being fitted in at least one of the plurality of holes whose inner circumferential surface has been finished by the major and minor cutting edges.
The major and minor cutting edges may be formed integrally with the land surface, or alternatively may be formed in a cutting tip which is removably fixed to the reamer. Further, the reamer may have an adjusting mechanism built therein which permits fine adjustment of position of the cutting tip (turning radius of the minor cutting edge).
In the finishing operation to the holes positioned in a line and axially-spaced apart from each other by the present method, a first one of the holes is machined as in a case where a hole is machined by an ordinary reamer, and then a second one of the holes is machined with the guide portion being interference-fitted or transition-fitted in the first hole which has been machined. Thus, while the second hole is machined, the guide portion of the reamer is guided by the first hole and is accordingly substantially unmovable in the radial direction. Since the second hole is machined by the major or minor cutting edge which is comparatively near from the guide portion accurately guided by the first hole, a sufficiently high degree of concentricity of the second hole with respect to the first hole and a sufficiently high degree of dimensional accuracy of the second hole are assured. In a process of manufacturing the reamer, if the major and minor cutting edges are formed integrally with the guide portion in a single step, it is possible to easily establish a minute difference between the turning radius of the land surface in the guide portion and the turning radius of the minor cutting edge. This eliminates a necessity of the fine adjustment of position of the cutting tip by the above-described adjusting mechanism which adjustment is not so easy for an ordinary operator and requires a skilled operator to be achieved.
The turning radius of the land surface in the axially-distal-end small-diameter portion and that in the guide portion may be determined such that the second and later holes are machined with the guide portion being interference- or transition-fitted in the hole or holes which has been machined, for assuring considerably high degrees of concentricity and machining accuracy. However, it is not essential that the guide portion is interference-fitted in the machined holes. That is, as long as the turning radius of the minor cutting edge is smaller than the turning radius of the land surface in the guide portion, the concentricity and machining accuracy can be improved as compared with the prior art.
(2) A method according to claim 1, wherein the number of the plurality of holes is at least three, and an inner circumferential surface of at least one of the plurality of holes is finished by the major and minor cutting edges, with the guide portion being fitted in at least two of the plurality of holes whose inner circumferential surfaces have been finished by the major and minor cutting edges.
Where the number of the holes to be machined is at least three, the first and second holes are machined as described above, and a third hole is then machined with the guide portion of the reamer being fitted in the first and second holes which have been machined. The third hole is thus machined while the guide portion is guided by the two points which are spaced apart from each other in the axial direction, thereby assuring a high degree of concentricity between the three holes. A fourth and later holes are also machined while the guide portion of the reamer is fitted in the holes which have been machined.
(3) A reamer comprising:
at least one land surface which is formed in an outer circumferential surface of the reamer and which extends from an axially distal end of the reamer toward an axially proximal end of the reamer;
an axially-distal-end small-diameter portion which extends over a predetermined axial distance from the axially distal end toward the axially proximal end;
a guide portion which is axially adjacent to the axially-distal-end small-diameter portion; and
major and minor cutting edges which are formed in at least one of the at least one land surface in the axially-distal-end small-diameter portion;
and wherein the at least one land surface has a turning radius which is smaller in the axially-distal-end small-diameter portion than in the guide portion, while the minor cutting edge has a turning radius which is larger than the turning radius of the at least one land surface in the axially-distal-end small-diameter portion and which is smaller than the turning radius of the at least one land surface in the guide portion.
The reamer according to the present mode (3) is suitable for practicing the inner-circumferential-surface finishing method defined above in mode (1).
(4) A reamer according to mode (3), wherein a difference between the turning radius of the at least one land surface in the guide portion and the turning radius of the minor cutting edge is not larger than 30 xcexcm.
The above-described difference should be larger as the turning radius of the minor cutting edge increases. However, in general, this difference is preferably not larger than 20 xcexcm, and more preferably not larger than 10 xcexcm.
(5) A reamer according to mode (3) or (4), wherein the major and minor cutting edges are constituted by a cutting tip which is fixed to an axially distal end of the axially-distal-end small-diameter portion, the cutting tip being formed of a sintered body having a hardness higher than that of cemented carbide.
In the reamer of this mode (5) in which the major and minor cutting edges are constituted by the cutting tip having a high hardness, the cutting sharpness or performance of the reamer is improved, thereby providing a further improved surface smoothness of the machined inner circumferential surface of the hole and a further improved dimensional accuracy of the hole. Moreover, the improved cutting performance leads to an improvement in the durability of the major and minor cutting edges and an accordingly prolonged life of the reamer. Where the major cutting edge is worn off, the cutting tip is, in general, re-ground at its distal, so as to be then used again. When the length of the cutting tip is reduced to a predetermined length as a result of repeated re-grindings, the cutting tip is discarded. The cutting tip may include a diamond coating which is formed by sintering an artificial diamond at an ultra-high temperature and an ultrahigh pressure, and a cemented carbide substrate which is covered by the diamond coating. Or alternatively, the cutting tip may include a CBN (cubic boron nitrides) sintered compact which is formed by bonding cubic boron nitrides to each other at an ultra-high temperature and an ultra-high pressure, and a cemented carbide substrate which is covered by the CBN sintered compact.
(6) A reamer according to any one of modes (3)-(5), wherein at least one of the minor cutting edge and the guide portion is back-tapered, and wherein the turning radius of the minor cutting edge represents a maximum turning radius of the minor cutting edge, while the turning radius of the at least one land surface in the guide portion represents a maximum turning radius of the at least one land surface in the guide portion.
It is not essential but preferable that the minor cutting edge is back-tapered such that the turning radius of the minor cutting edge decreases as the minor cutting edge extends from the axially distal end of the reamer toward the axially proximal end of the reamer. It might not be preferable that the guide portion is not back-tapered, in view of a guiding performance of the guide portion of the reamer. However, the guide portion may be slightly tapered, in order to avoid an increase in the diameter of the guide portion in the direction away from the axially distal end toward the axially proximal end. Where the minor cutting edge and the guide portion are both back-tapered, the difference defined in the mode (4) represents a difference between the maximum turning radius of the minor cutting edge and that of the land surface in the guide portion, namely, between the turning radius of the minor cutting edge at its distal end and that of the land surface at the axial end of the guide portion which end is nearest to the axially distal end of the reamer.
(7) A reamer according to any one of modes (3)-(6), wherein the at least one land surface includes a plurality of land surfaces, and wherein an angular interval between each circumferentially adjacent two of the plurality of land surfaces in a first region is smaller than that in a second region, the first region corresponding to one of opposite sides of a plane containing an axis of the reamer and an intersection of the major and minor cutting edges on which side one of the plurality of land surfaces having major and minor cutting edges formed therein is located, the second region corresponding to the other side of the plane.
When the reamer is in the process of cutting an inner circumferential surface of a hole by the major and minor cutting edges, the land surfaces are supported by the inner circumferential surface of the hole, thereby preventing the reamer from being deflected due to a cutting resistance acting on the major and minor cutting edges. Since the cutting resistance tends to be increased and decreased, it is preferable to prevent the reamer from being deflected not only in a cutting-resistance-acting direction in which the reamer is forced to be deflected by the cutting resistance but also in a direction opposite to the cutting-resistance-acting direction. In this view, the land surfaces are preferably provided both in the first and second regions. Further, the provision of the land surfaces in both of the first and second regions is preferable, also for easier definition of the position of the axis of the reamer. However, it is not preferable that the number of the land surfaces increases, in view that a frictional resistance acting on the land surfaces increases as the number of the land surfaces increases. Therefore, it is preferable to increase the total circumferential area of the land surfaces in the first region on which the cutting resistance principally acts and to decrease that of the land surfaces in the second region.
(8) A reamer according to any one of modes (3)-(7), wherein one of the plurality of land surfaces is diametrically opposed to one of the plurality of land surfaces which has major and minor cutting edges formed therein.
(9) A reamer according to mode (8), wherein two of the plurality of land surfaces are located in the first region in addition to the one which has major and minor cutting edge formed therein, while one of the plurality of land surfaces is located in the second region in addition to the one diametrically opposed to the which has major and minor cutting edge formed therein.
(10) A reamer according to any one of modes (3)-(6), wherein the number of the at least one land surface is one.
(11) A reamer according to any one of modes (3)-(10), wherein the at least one land surface extends straight in parallel with an axis of the reamer.
(12) A reamer according to any one of modes (3)-(10), wherein the at least one land surface is a spiral land surface which is twisted around an axis of the reamer.
(13) A reamer assembly comprising:
the reamer recited in any one of modes (3)-(12); and
a reamer holder which holds the axially proximal end of the reamer, and which is to be mounted in a spindle of a machine tool.
The reamer has to be equally positioned relative to the spindle, each time the reamer is newly installed in the spindle of a machine tool. To this end, the reamer has to have at its axially proximal end a high-precision holding portion which permits the reamer to be removably attached at the holding portion to the spindle with a high repeatability of the positional relationship between the reamer and the spindle. Where the holding portion is constituted by the reamer holder which is separable from the reamer, the reamer holder can be used as a holder commonly for a plurality of different reamers, thereby making it possible to reduce the tooling cost.
(14) A reamer assembly according to mode (13), further comprising an alignment mechanism which is provided between the reamer and the reamer holder, and which decreases at least one of a radial deviation of an axis of the reamer from an axis of the reamer holder and an inclination of the axis of the reamer with respect to the axis of the reamer holder.
Where the reamer is separable from the reamer holder, it is preferable that the position of the reamer relative to the reamer holder is adjustable upon attachment of the reamer to the reamer holder. The reamer and the reamer holder may have, for example, a fitting boss and a fitting hole formed in the respective end faces, such that the reamer and the reamer holder are connected with each other by engagement between the fitting boss and the fitting hole, thereby positioning the axis of the reamer and that of the reamer holder relative to each other. However, a required degree of coaxial relationship between the reamer and the reamer holder and a required degree of machining accuracy are not necessarily assured by only the engagement of the fitting boss and hole, particularly when theses required degrees are considerably high.
(15) A reamer assembly according to mode (14), wherein the reamer further includes a flange which is attached to the axially proximal end of the reamer and projects radially outwardly from the axially proximal end of the reamer, and at least three axially adjusting screws and at least three screw bolts which are provided in the flange and which constitute the alignment mechanism for decreasing the inclination of the axis of the reamer with respect to the axis of the reamer holder, the axially adjusting screws being arranged about the axis and equi-angularly spaced apart from each other in a circumferential direction of the reamer so as to be abuttable on an end face of the reamer holder, each of the screw bolts being positioned between circumferentially adjacent two of the axially adjusting screws.
(16) A reamer assembly according to any one of modes (13)-(15), wherein the reamer has a fitting boss while the reamer holder has a fitting hole so that the reamer and the reamer holder are connected with each other by axial engagement between the fitting boss and the fitting hole, and wherein the reamer holder includes at least three radially adjusting screws which are provided in a circumferential wall of the reamer holder circumferentially defining the fitting hole and which constitute the alignment mechanism for decreasing the radial deviation of the axis of the reamer from the axis of the reamer holder, the at least three radially adjusting screws being equi-angularly spaced apart from each other in a circumferential direction of the reamer holder, so as to be abuttable on an outer circumferential surface of the fitting boss.